Generally, with each engine of a transport plane is associated a supervising unit which comprises in particular:                a means of regulation for acting on the speed of the engine, as a function of control orders received. This means of regulation is able to adjust the flow rate of fuel intended to supply the engine; and        a computation unit, for example an engine electronic regulator of the EEC (“Electronic Engine Control”) type, which determines the control orders for said means of regulation.        
This computation unit uses in particular information relating to the conditions under which the aircraft is maneuvering, that is to say information relating to aerodynamic parameters such as the static and total temperatures and/or the static and total pressures, to determine these control orders. For safety reasons, said computation unit uses several different sources to obtain this information, namely generally:                an engine sensor, which is able to measure on the engine the value of the relevant aerodynamic parameter; and        two airplane sources, for example of the ADIRU (“Air Data Inertial Reference Unit”) type, which also have access to values of this aerodynamic parameter and which are connected individually by specific links, for example of ARINC 429 type, to said computation unit.        
The computation unit must therefore select, from the various values of the aerodynamic parameter that it receives, that one which it will use for its computations.
In certain situations, a poor selection is possible, which may have very damaging effects. Specifically, an erroneous item of information which is not representative of the actual flight conditions of the aircraft brings about an erroneous computation of the engine speed so that the engine may then be led to operate in a mode inappropriate for said flight conditions. It may then even stop, for example when the speed demanded is too low for the conditions encountered.